Electronic packaging technologies used in various steps involved in the process of preparing a variety of electronic products using semiconductor devices are very important for the reason that the performance characteristics, size, price, reliability, and durability of the final products depend thereon.
In response to the recent trend of making the gap narrower and the connection density higher, it has become essential in the field of packaging semiconductor or display that a plurality of electrodes formed in a narrow gap can be simultaneously connected. Accordingly, in the liquid crystalline display (LCD) packaging field, an electroconductive adhesive is employed in order to form a mechanical and electrical connection between the access printed circuit boards and transparent electrodes.
Such an electroconductive adhesive is generally used in the form of an anisotropic conductive film (AFC) or an isotropic conductive adhesive (ICA), preferably an anisotropic conductive film composed of electroconductive particles dispersed in a thermosetting or thermoplastic insulation resin.
There have been used as electroconductive particles that function as an electroconductor, carbon-based powders or fibers, solder balls of e.g., Ag, and nickel (Ni) particles or polymer balls coated with Ni.
Nickel used as electroconductive particles of an anisotropic conductive film is not expensive and has a relatively good electroconductivity, but it tends to undergo erosion or oxidation when exposed to a high temperature/high humidity condition. A method of coating nickel particles with gold (Au) was suggested in order to solve such a problem. Also, a method has recently developed to coat polystyrene particles comprising crosslinking monomer, e.g., divinylbenzene, with nickel, and coat the coated Ni particles with gold.
However, electroconductive particles that consist of polymer microparticles coated with a metal also have several problems in that: they have poor long-term stability of the conductivity and of the mechanical properties because of the low interfacial bonding strength between the polymer microparticles and the metallic coating layer; and their production is costly and generates a large amount of environmentally harmful materials.
One of the conventional electroconductive particles, which is prepared by a method comprising the step of disposing a metal on the surface of a polymer microparticle by pressurizing and heating to form a conductive region, also has the problem that the metallic coating layer is easily cracked and peeled off from the polymer microparticle. Accordingly, an anisotropic conductive film composed of such conventional electroconductive particles dispersed in an insulation resin is hampered by high contact resistance and low reliability.
Therefore, there exists a need to develop an electroconductive particle having improved performance characteristics in terms of long-term stability of conductivity, surface conductivity, durability, and thermal resistance, which is devoid of the problems associated with the conventional particles having low conductivity due to the generation of cracks and exfoliation between the polymer microparticle and the metal layer, and is able to maintain a high electroconductivity at a high temperature of 100° C. or more.